The Mets manager said before Friday’s 7-2 loss to the Diamondbacks that he could be on the verge of dropping the team’s six-man rotation, after only one turn through.

“It’s a pain in the [butt] — literally,” Collins said before the Mets faced the Diamondbacks at Chase Field. “I’m just tired of answering the questions, so we could be going back to a traditional rotation.”

Jon Niese, who had posted a 9.00 ERA over his previous four starts, wasn’t pitching for his job on Friday, according to Collins. In six innings, he allowed three earned runs on six hits, walked one and struck out eight.

By process of elimination, that could leave Dillon Gee as the man out. Collins said “possibly” somebody would be headed to the bullpen.

The Mets implemented the six-man rotation to preserve innings for Matt Harvey, Jacob deGrom and Noah Syndergaard. It is unclear how the Mets will proceed with their young guns if the six-man rotation is dropped. In recent weeks, the other options presented by Collins were shutting down pitchers in September or giving them two-week breaks in the middle of the season.

Gee said he hasn’t been told anything about his next possible start. Told Collins was considering ditching the six-man rotation, Gee said: “It doesn’t surprise me.”

Though he didn’t get the win, Steven Matz had another brilliant performance for Triple-A Las Vegas.

The lefty allowed just one run (a solo homer) on seven hits in six innings but was the hard-luck loser in a 1-0 defeat to Memphis. Matz also struck out five in his 97-pitch outing, and his Pacific Coast-leading ERA fell to 1.94.

The game was called with one out in the seventh because of rain.

Jeurys Familia wasn’t needed after logging a five-out save the previous night. The righty also recorded a five-out save in his previous appearance, on Sunday against the Marlins.

“He is another guy that is an endangered species, so we’ve got to be careful with him,” Collins said.

Familia, who has a 1.35 ERA and 16 saves in 17 chances, has arguably been the team’s MVP this season, after Jenrry Mejia was lost to an 80-game PED suspension.

“You go back to where [Familia] was 13 months ago,” Collins said. “There were discussions about sending him back to the minor leagues. He was struggling with his command, he wasn’t getting anybody out. And a year later he’s in my opinion one of the top relievers in all of baseball, so his growth and development has been off the charts.”

The Mets entered Friday in sole possession of first place, but fell one-half game behind the Nationals, 7-5 winners over the Cubs. It was the deepest into a season the Mets had been alone in first place since Sept. 19, 2008, when they held a half-game lead over the Phillies.